The easiest and safest way to back up your Operating System is to create a System Image. Only install Windows and a minimum of other programs on the partition. My Windows partition is 200 Gigabytes a little over 100 Gigabytes is used.
I use EaseUS Todo backup to create the image. It's Free, very easy to use and has worked for me for many years, I started using it when I was beta testing Windows 7.
It will simply restore the entire partition and everything on it, including the Boot Sector. Don't put your Data or Software on the Windows Partition, and it will create the bootable media to start your computer and run the process in minutes.
My computer has 3 internal hard drives 5, partitions, and one external hard drive. If it doesn't boot, has malware or corrupted files I can fix it in about 20 minutes. You can store the backup file anyplace other that the Windows partition.
Once restored, the computer will run just as it did, nothing else has to be reinstalled or recovered. A complete fix in less than half an hour.
Everyone should have a System Image of their OS.